In the conventional fourdrinier papermaking process, a water slurry, or suspension, of cellulosic fibers (known as the paper “stock”) is fed onto the top of the upper run of an endless belt of woven wire and/or synthetic material that travels between two or more rollers. The belt, often referred to as a “forming fabric,” provides a papermaking surface on the upper surface of its upper run which operates as a filter to separate the cellulosic fibers of the paper stock from the aqueous medium, thereby forming a wet paper web. The aqueous medium drains through mesh openings of the forming fabric, known as drainage holes, by gravity alone or with assistance from one or more suction boxes located on the lower surface (i.e., the “machine side”) of the upper run of the fabric.
After leaving the forming section, the paper web is transferred to a press section of the paper machine, in which it is passed through the nips of one or more pairs of pressure rollers covered with another fabric, typically referred to as a “press felt.” Pressure from the rollers removes additional moisture from the web; the moisture removal is often enhanced by the presence of a “batt” layer on the press felt. The paper is then conveyed to a dryer section for further moisture removal. After drying, the paper is ready for secondary processing and packaging.
Press felts typically include one or more base fabric layers; these can be “flat-woven” and formed after weaving into an endless belt, or can be woven in endless form.
Of course, weaving a fabric of a base layer requires that provision be made for joining it into endless belts. Such joints should be constructed in such a manner that they are sufficiently strong to withstand the extreme load, temperature, and wear conditions the press felt experiences, yet do not cause the surface of the press felt above the seam to unduly mark the paper. One popular method of joining the base fabric of a press felt is to form loops with machine direction yarns on each end of the base fabric. To form the base fabric into an endless belt, the ends of the fabric are placed adjacent to each other, with each of the loops on one end positioned between two loops on the other end in interdigitating fashion. A “pin” (usually formed of a single monofilament or monofilament strands) is then inserted into all of the loops to join the ends. After the batt layer(s) are needled or otherwise attached to the base layer, the batt layer(s) are cut at the seam location, the pin is removed, and the finished press felt is shipped to a paper mill. Once at the paper mill, the press felt can be installed by placing it onto a paper machine, then inserting another (usually more flexible) monofilament pin or pintle into the loops. Examples of this type of seam are described in U.S. Pat. Nos. 4,764,417 and 4,737,241 to Gulya; U.S. Pat. No. 4,601,785 to Lilja et al.; U.S. Pat. No. 5,476,123 to Rydin, and U.S. Pat. No. 7,135,093 to Gstrein, the disclosures of which are hereby incorporated herein by reference in their entireties.
Base fabrics of press felts have taken a variety of configurations. In one configuration, the “fabric” is actually two separate fabrics that form a total of three layers. The bottom fabric is a double layer fabric that provides the seam loops, with the top fabric being a single layer fabric that is cut after weaving, combination with the bottom fabric, and needling of an overlying batt layer. An exemplary press felt of this configuration is shown in International Patent Application No. WO 0017433, the disclosure of which is hereby incorporated herein in its entirety. One apparent disadvantage of a fabric of this configuration is the need to cut the top fabric layer, which then has loose ends that can impact the manner in which the overlying batt lays over the fabric.